Variation in the Weight-to-Length Relationship among Florida and Northern Largemouth Bass and Their Intraspecific F1Hybrid

Abstract

Weight–length regression equations and relative weights (Wr, the ratio of measured weights to standard weights at length) were compared among 1,401 electrophoretically assayed Florida largemouth bass Micropterus salmoides floridanus, northern largemouth bass M. s. salmoides, and their first-generation (F1) intraspecific hybrid in Aquilla Lake, Texas. Small Florida largemouth bass (101–300 mm total length, TL) displayed lower Wr values than small northern largemouth bass. Differences in Wr were not apparent between 301 and 500 mm TL. Significant subspecific differences in the weight–length slope and intercept coefficients were consonant with observed variation in Wr values. Among four year classes, seasonal differences in subspecific Wr consistently varied five to nine units for fish of age 1 and younger. Relative weight values for small F1 hybrids (101–200 mm TL) were intermediate between those of the two subspecies; they were similar to those of northern largemouth bass but higher than values for the Florida subspecies at 201–300 mm TL. There was no evidence that lower winter temperatures in Aquilla Lake compared to those measured in Florida caused a decline in Florida largemouth bass condition. At smaller sizes, subspecific discrepancies in the weight–length relationship appeared to be genetically inherent. If condition indices are used to evaluate phenotypic performance in largemouth bass populations stocked with the alternative subspecies, these differences should be considered.